31 



On the Geological Structure and Physical 

 Features of Central Australia. 



Ry J. J. East, Corresponding Member. 



[Read April 2, 1SS9.] 



Plate III. 



TOPOGRAPHY. 



In following the Overland Telegraph Line northward from the 

 Flinders to the Macdonnell Ranges, the route traverses the Lake 

 Eyre basin, and ascends a gentle slope to an elevated region in 

 the heart of the continent. 



Three principal divisions of country present themselves along 

 the route, and may be termed^ — - 



I. " The Great Austral Plain." — A vast region of inconsider- 



able elevation, wdth some portions especially low-lying, 

 and descending at the surface of Lake Eyre to about 

 20 feet below sea level. 



II. " The Terraces." — The slopes and low^ parallel ranges 



which border the plain and form, as it were, a flanking 

 terraced formation to 



III. " The Great Central Plateau," whose furrowed southern 

 face develops the system of narrow ridges collectively 

 known as the Macdonnell Ranges. 



AVithin the tirst division, and west of Lake Eyre, stands the 

 Denison or Peake Ranges. They rise like islands from out of a 

 plain of sands and clays, and are outlying portions of the Flinders 

 Range. 



I. The Great Austral Plaix. 



The surface contour is a level plain, with the horizon in every 

 direction more or less broken by low flat-topped hills of uniform 

 height, shaped like truncated cones, or else a low precipitous 

 blutf, uniform in height with the cones, and forming the escarp- 

 ment of a small " tableland " a few miles in area. 



The hills and blutts are almost destitute of vegetation. The 

 arborescent growth is limited to acacia bushes, a stunted Eucalypt 

 locally termed the " Box " or " Coolibah," and the crooked 

 " Gidgia," a wonderful specimen of vegetable contortion ; whilst 

 on the plain, trees are rarely seen, but the hardy saltbush and 

 cotton-bush abound for miles. Large patches of the level plains 

 near the hills are perfectly sterile, and are covered wdth a 



